It is well-known to treat polyamide substrates, such as carpeting, with compositions which impart resistance to staining by an acid dye, such as FD&C Red Dye No. 40. Such compositions are commonly referred to as stain-resists or stain-resist agents.
For example, one class of known stain-resist agents comprises one or more sulfonated hydroxyaromatic-formaldehyde condensation products, for example, phenol-formaldehyde condensation products or formaldehyde-naphthol condensates. When stain-resist agents based on such condensation products are applied to polyamide substrates, they provide acid dye stain-resistance which resists removal by shampooing. But such treated substrates are prone to yellowing on exposure to ultraviolet light (UV) or to nitrogen oxides (NO.sub.x), or to combinations of UV and NO.sub.x exposure.
Another class of known stain-resists involves the use of carboxyl group-containing polymers; for example, methacrylic acid homopolymers and copolymers. Due to the ionic character of carboxy group-containing stain-resist agents, polyamide fiber substrates treated with such stain-resists tend to be sensitive to high pH values, such as those that may often be encountered in commercial rug shampoos. As a result, in some cases, stain-resistance is partially or completely lost following shampooing. The carboxy-group-containing stain-resist agents show better resistance to yellowing on exposure to UV or NO.sub.x or a combination of UV and NO.sub.x, but poorer resistance to removal by shampooing than the sulfonated phenol-formaldehyde condensates.
Compositions based on sulfonated phenol-formaldehyde condensates combined with polymers of methacrylic acid or hydrolyzed copolymers of maleic anhydride and ethylenically unsaturated compounds, when applied to polyamide substrates, will provide resistance to staining by acid dyes. While some improvement is also obtained in resistance to yellowing caused by UV and/or NO.sub.x and resistance to removal by commercial shampooing, it is far from optimum.
Yet another class of stain-resist agents comprises products prepared by polymerizing methacrylic acid, or methacrylic acid and one or more ethylenically unsaturated comonomers in the presence of sulfonated aromatic formaldehyde condensates. While the carboxylic acid-containing stain-resist agents overcome some of the discoloration problem caused by UV and/or NO.sub.x, they lack adequate resistance to removal in commercial shampooing.
Epoxy resins can be cured with carboxylic or polycarboxylic acids, and epoxy resins in combination with carboxylic acid-containing polymers can be applied to fiber substrates. For example, combinations of epoxy resins and copolymers of methacrylic acid have been applied to carpets and carpet yarns as anti-soilants for carpets and carpet yarns. However, unsatisfactory performance was reported for poly(methacrylic acid) or copolymers with more than 75 wt. % of methacrylic acid, with or without epoxy resins. Moreover, there is no disclosure of using such compositions for imparting to polyamide substrates resistance to staining caused by acid dyes.
In view of the above-described considerations, it is apparent that there is a need to provide stain-resists for polyamide substrates which combine resistance to removal during commercial shampooing and resistance to yellowing caused by UV or NO.sub.x or both.